Prime-Numbers.md

7.2 All Prime Numbers

the problem

Ask the user to enter a number. Then find all the primes up to that number.

Hints

You can use the previous is_prime function that you created in the previous problem. Now create a new function named all_primes. In that function, run a for loop.

For each number, call the is_prime function. If the return is True to add it in the prime list.

The Solution

 def is_prime(num):
  for i in range(2,num):
      if (num % i) == 0:
          return False
  return True
 
def all_primes(num):
  primes = []
  for n in range(2,num+1):
      if is_prime(n) is True:
          primes.append(n)
  return primes
 
num = int(input("Enter upper limit: "))
primes = all_primes(num)
print(primes)

Try it on Programming Hero

Explanation

The first one is the is_prime that you have seen before. Now we created another function named all_primes. In the all_primes function, we create a list named primes to hold the prime numbers. Then run a for loop using range.

The range starts at 2 and runs until num+1 so that it goes until num. We are starting at 2. Because 2 is the first prime number.

Inside the loop, call the is_prime function and check the return. If the return is True then append the n in the primes list.

Then return the primes list.

That’s it.

   

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